In the area of fluid bed technology it is a well-known problem that condensation is generated on the walls and the ceiling of the housing due to the high moisture content of the fluidizing gas after the passage through the layer of material to be processed in the fluid bed. It is a further problem that products may deposit on these walls.
In order to remedy these problems it is known, as eg. described in U.S. Pat. No. 4,492,040 (Niro), to provide the inner side of the housing with heating means, eg. heating panels which are heated in a suitable manner, for example by means of electric current, heated gas or air, or steam or water, in order to avoid condensation and deposition of products on the walls and ceiling of the housing.
Furthermore, it is known to direct a so-called bypass gas to the fluid bed, which is mixed with the fluidizing gas in order to obtain a gas mixture having a lower moisture content in order to avoid condensation in the discharge system of the fluid bed apparatus.
However, in fluidization processes involving materials which during the drying release corrosive vapour, such as eg. s-PVC which releases HCl, the above-mentioned measures may not be sufficient.